‘Tis the Season for Sea Ice

The news lately is replete with mentions of sea ice, because NOAA’s Arctic Report Card features it prominently, mentioning that “In 2018 Arctic sea ice remained younger, thinner, and covered less area than in the past. The 12 lowest extents in the satellite record have occurred in the last 12 years.” It also emphasizes how the loss of Arctic sea ice is but the start of a chain of events leading to dramatic change both in the Arctic and elsewhere.


For those of us who keep track of Arctic sea ice, this is a story we know well. Of course some news reports have treated it all as a stunning revelation, but the NOAA report is highlighting trends that we’ve known about for years, decades even. Rather interesting is what they have to say about the changes of ice age:


Older ice tends to be thicker and is thus more resilient to changes in atmospheric and oceanic heat content compared to younger, thinner ice. The oldest ice (> 4 years old) continues to make up a small fraction of the Arctic ice pack in March, when the sea ice extent has been at its maximum in most years of the satellite record. In 1985, the oldest ice comprised 16% of the ice pack (Fig. 3a), whereas in March of 2018 old ice only constituted 0.9% of the ice pack (Fig.3b). Therefore, the oldest ice extent declined from 2.54 million km2 in March 1985 to 0.13 million km2 in March 2018, representing a 95% reduction.

The decrease from 2.54 to 0.13 is significant in every sense of the word.

I’d like to look at how Arctic sea ice has changed by season, but I’m going to re-define the seasons. The reason we usually think of summer as being the months Jun-Jul-Aug is that those are the three hottest months of the year (for us northern-hemisphere people). Let’s define a “sea ice summer/fall” as the three months with lowest sea ice extent. We can figure that out from a plot of sea ice against month of the year (rather than time). I’ll make a boxplot by month, which gives this:

We can see that the three lowest-extent months are Aug-Sep-Oct, so we’ll call that our “sea ice summer/autumn.” Similarly, we’ll define autumn/winter as Nov-Dec-Jan, winter-spring as Feb-Mar-Apr, and spring/summer as May-Jun-Jul. Now I can compute the yearly average sea ice extent for each season separately.

I wasn’t exaggerating when I mentioned our knowing for decades about sea ice trends. Let’s begin by looking for trends using only the data prior to the year 2000. The changing extents (transformed into anomalies, and with a separate line for each season) look like this:

First, they’re all trending downward, and all trends turn out to be statistically significant. We knew by 2000 (even before that, in fact) that Arctic sea ice was in decline during every season. Second, the summer/autumn extent, during the season of least sea ice, shows a lot more variation than the other seasons. Its trend isn’t declining any faster, but the size of the fluctuations is considerably greater.

Let’s re-draw that same graph, but with some extra room added, and I’ll put in the trend lines for each season, extended from year 2000 up to the present:

And what has happened since year 2000, you wonder? This:

First, the already-significant downward trends didn’t just continue, they got more severe. Second, the summer/autumn extent continued to show a lot more variation than the other seasons.

The most important information about sea ice in the Arctic Report Card is that its changes really are just the beginning of a chain of events, a cascade which has already had unpleasant consequences. It’s beyond our ken to fathom all of the future consequences, but some of the possibilities are truly frightening (e.g. permafrost melt).

Meanwhile at the global warming denier blog WUWT, Eric Worral can twist a NASA report from “increases in the rate at which Arctic sea ice grows in the winter may have partially slowed down the decline of the Arctic sea ice cover” into “Global Warming Promotes Arctic Sea Ice Growth.” What a rube.


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16 responses to “‘Tis the Season for Sea Ice

  1. ch ch ch changes…. Still don’t know what I was waitin’ for
    And my time was runnin’ wild… turn and face the strange

    I think the changes in the Arctic ice are locked in now for thousands of years and this has large consequences for the weather in the northern hemisphere. We are headed toward a world without an Arctic icecap and that is not a world that our species has ever known. Turn and face the strange, I guess.

    • Yes and no, sbm. The modeling seems to show–and yes, I think that the final words in modeling ASI are yet to be written, so a grain of salt is warranted–that the ice could recover, even from a seasonal ice-free state, given appropriate forcings, especially GHGs. That’s the good news–the sea ice feedback appears not to be so strong as to be, by itself, a determinative ‘tipping point.’

      The bad news is that since higher GHG levels are locked in, and since emissions growth is still continuing, and since we have a poor international political environment for urgently-needed mitigation improvements, the ability of the ice to recover is probably not going to be tested in the real world any time soon. But you knew all that, of course, as do most of us here.

      Still fighting for “less bad,” I remain yours truly, etc., etc.–

      • you da man, Doc! I have no objection to optimism and hope for recovery of sea ice. That’s why I say “I think” when I post. I am not claiming my thoughts are factual or correct, they are simply the product of my analysis and light reading.

        I recall for the past few years that numerous folks here and at RC got pushy with me when I shared my thoughts that fossil fuel emissions had not peaked as others thought had happened with the stagnation of increase rate over the past couple of years. I don’t remember exactly who those folks were now, maybe Al Rodgers? Hank Roberts? Whoever they are, they are not speaking up now that the recent emission report has hit the fan and shows significant increase that suggests we have not yet peaked.

        Kind of same thing here, but you are cordial, as always, with your hopes and posts. If you and I are still alive and typing when the Arctic Sea ice is gone, we can both say, well, that’s a shame. Too bad it worked out that way.

        Cheers

        Mike

      • Thanks, sbm. I hope that before that we’ll have hard evidence of a downward bend in the emissions curve.

        Clearly, it’s not a given, but I believe with all my heart that it can be done.

  2. Reblogged this on jpratt27 and commented:
    Hard to deny global warming

  3. Cryosphere Today used to have a graph of sea ice extent going back to 1900 which is interesting to compare to your up to date data. The site is now offline but I found the graph on the wayback machine here:

    According to that graph the decline in summer sea ice (JAS) started well before 1980, possibly as early as 1950 (by eyeball). Spring sea ice decline (AMJ) also started before 1980. That graph might look interesting in the OP. The data come from a peer reviewed article but I do not know the reference.

  4. And speaking of impacts in general, this piece, from PBS News Hour, is one of the best I’ve seen:

    https://www.pbs.org/newshour/show/to-save-its-future-will-this-md-town-have-to-destroy-its-historic-business-district

    The focus is on the 2 ‘once in a lifetime’ floods that devastated Ellicot City within just a few years, but it does make connections to other climate-related disasters in recent news–and it’s rather interesting that it’s not the reporter who sums it up, it’s the people who experienced the flooding, and who are the focii of the story.

  5. Susan Anderson

    Meanwhile, East Antarctica is beginning to melt:
    https://www.bbc.com/news/science-environment-46517396
    [brief extract of opening; best go to link for graphics and video:] Nasa says it has detected the first signs of significant melting in a swathe of glaciers in East Antarctica.
    ….
    But satellites have now shown that ice streams running into the ocean along one-eighth of the eastern coastline have thinned and sped up.

    There’s a note this was presented at the AGU conference.

  6. The serious comment that the cretin Eric Worral has mis-represented for the eager denialists on the planet Wattsupia is this NASA news item. The research being discussed is Petty et al (2018) ‘Warm Arctic, Increased Winter Sea Ice Growth?’ The talk of feedback mechanisms resisting the loss of Arctic Sea Ice is described as simply the extra volume of winter freeze resulting when the ice is thin and less able to insulate the water beneath which is thus going to freeze more than it would under thicker ice. It’s a sort of zombie mechanism that will keep ASI from quickly dying away as temperatures rise – an un-dead zombie phase of Arctic Sea Ice loss.

    • Yeah, this has been a minor-league denial meme for at least a couple of years–as if it were a mystery that with vast swathes of newly open water, one sees more water freeze when the sun goes down for the long Arctic night.

      (And of course, what you said about the parallel ‘thin ice’ case, Al.)

      The will not to understand is a remarkable thing. Too bad it’s also a dangerous one.

    • Here’s a 2011 paper on those processes:
      https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010GL045698

      I like Petty’s new paper, it uses newly available satellite data and model runs to investigate this in a more realistic way.

      The WUWT article mostly quotes other people and then adds some snark showing they didn’t understand anything about the topic.

  7. Worral spends his time misleading and trolling on Quora.com as well. I’ve bumped up against him a few times there. I didn’t realise he was a big enough cheese to get published on WUWT, but I guess the bar isn’t very high these days. The power of people to ignore reality and stick to their preconceptions never ceases to amaze me, especially the way it actually afflicts quite smart people: it’s the opposite of stupidity I recall someone doing a study on this a while back – smarter people make better/more committed contrarians/conspiracists/deniers).

    • Reminds me of an observation my wife has made more than once. She’s a career teacher in special education, and specifically EBD/SEBD–that is, [Severe] Emotional and Behavioral Disturbance. Some of her students had generalized or specific learning disabilities, but a large proportion had raw abilities probably in the ‘gifted’ range.

      Her take on that (paraphrased) was “It takes a smart kid to figure out so well and so quickly just which adult buttons they can push for maximum disruption.” (“Meat space” trolling, basically.) The fundamental dysfunction in such cases is emotional/behavioral–not cognitive.

  8. rhymeswithgoalie

    Arctic ice at its minimum is much more responsive to the local weather patterns, such that a year like 2012 with a cyclone to push and stack the loose ice shows a much lower sea ice extent.

    [Tangent: One of the problem with once-vaunted Arctic Ocean drilling is the increasing mobility of pack ice, such that fixed rigs are vulnerable to collisions and have to spend costly downtime any time they are potentially threatened by the movement of a large or fast mass.]

  9. “Second, the summer/autumn extent, during the season of least sea ice, shows a lot more variation than the other seasons. Its trend isn’t declining any faster, but the size of the fluctuations is considerably greater.”

    The fall/winter/spring ice is constrained against land borders.

    • Good observation, but I think that may not be the only reason, since May is pretty reliably the least variable month, yet its extent is only 5th-greatest. But I’m lacking any good hypotheses about why that might be, so you’re still way ahead of me on points!